Eating arsenic-based life forms? I'll leave that for you. I know you're just joking, but If by some inconceivable chance they do exist, one pretty good guess at why they're still here is that arsenic is extremely toxic, which as far as biological defenses go is a pretty good one.

I had just read about this possibility today in this book [amazon.com], a fascinating compendium of mini-essays by leading thinkers about scientific or social developments that may be around the corner. Existing tests for biological organisms are geared towards a working asssumption that life forms will be part of the basic, familiar biological tree that we are based on. A "shadow biosphere" was discussed as something that could potentially be an alternative hierarchy of life, so unfamiliar that we haven't understood how to look for it even though it could be relatively populous in certain niche areas of the earth.

Finding an alternative pathway to the evolution of complex life forms could affect our perception of how common life is in the universe and could be a stunning treasure trove of discovery and insight for biologists.

Just FYI, Mono Lake lies in an area that's still quite volcanically active, with many hot springs and fumaroles including a couple that can be seen right from U.S. Route 395, the main highway that runs through the region. In fact, the Long Valley area you mentioned is the caldera of a potential super volcano.

The whole area is also very beautiful in an almost other-worldly way. It looks sort of like one of the better Star Trek (TOS) sets.

Probably. Arsenic is toxic to us because of its chemical similarity to phosphorous. It reacts enough like phosphorous to get pulled into various reactions in our cells, and then enough differently to make the processes fail. In an organism that used arsenic instead of phosphorous, phosphorous would cause the same trouble.

Computer analogy -- In the old Eastern Bloc, clones of Western chips were reportedly made using "metric inches" of 25 millimeters instead of American inches of 25.4 mm. This worked fine electrically and mechanically when all the gear you were using was made to the same spec, but if you unknowingly tried to put a Western-made chip on 1/10th inch spacing into an Eastern Bloc socket on 2.5 mm spacing, or vice-versa, the incompatibility could cause failures. Similarly, it might be possible to build a cellular chemistry using arsenic instead of phosphorous. But if you put arsenic into a creature built with phosphorous or vice-versa, you're likely going to have failures as the cell unknowingly plugs the wrong element in.

The other thing that struck me about TFA is that maybe she is a bit limited in her approach: Sugars and vitamins are all fine, but just beacuse they're mostly beneficial to "actual" life doesn't mean that they are to (hypothetical) "alternate" life. Maybe she's inadvertently killing whatever stuff there is in her water buckets? She should try mixing in other stuff as well.

Come to think of it, small humans often react "Vitamins!?! Aarrrrgh!". They do seem to tolerate sugar pretty well though.